Oil burner safety control



Oct. 28, 1958 G. M. RUSSELL 2,857,960

' OIL BURNER SAFETY CONTROL Filed Nov. 27, 1956 3 Sheets-Sheet l I l\. I. II I I I I 5 w l- I l 2 I Q I I i g I I II \I N I N I a N 3 i U z E I E' I (n 5g NU t :35 |no SI 0 t 2 U 0 I- 5 51 m g. 3 $2 I A 0 7 INVENTOR.

GROVER M. RUSSELL WWQW ATTORNEY Oct. 28, 1958 G. MRussELL 2,857,950

OIL BURNER SAFETY CONTROL Filed Nov. 27, 1956 s Sheets-Sheet 2 INVEN TOR. GROVER M. RUSSELL WW a. aim

ATTORNEY Ogt. 28, 1958 GM. RUSSELL OIL BURNER SAFETY CONTROL Filed Nov. 27, 1956 3 Sheets-Sheet 3 4INVENTOR. GROVER M. RUSSELL WWQQwM ATTORNEY United States Patent OIL BURNER SAFETY CONTROL Grover M. Russell, Goshen, Ind., assignor to Penn (Controls, Inc., Goshen, Ind., a corporation of Indiana Application November 27, 1956, Serial No. 624,641

6 Claims. (Cl. 158-28) This invention relates generally to control apparatus for a burner and in particular to a control for proper sequencing of ignition and combustion in a domestic oil burner.

The required operational sequence of modern oil burners has, customarily, been accomplished by a primary control which includes a relay to operate a power circuit to the burner motor, an electrothermally operated safety switch, and, in types for controlling burners with intermittent ignition, a second electrothermally operated switch for terminating the operation of the igniter. This second thermally operated switch may, in addition, serve to operate additional switches in the control circuit to provide proper sequencing of the circuit operations.

The safety switch, referred to above, is usually of the warp switch lockout type and, once moved to its open position is there locked, by a suitable mechanism, until it is manually reclosed or reset by actuation of a pushbutton, or similar operation, which is located at the primary control, which, in turn, is usually located adjacent the oil burner itself.

The safety switches heretofore used in oil burner primary controls have been as previously pointed out, of the lockout type, its contact never being opened by its electrothermal operator except when a malfunction has occurred in the burner operating sequence. Under such conditions the safety switch is subject to a defect, which can be highly dangerous. This defect in safety switches and their operating circuits is common to most safety devices, including high temperature cut-outs and high pressure relief valves on domestic water heaters, safety pilot valves for gas appliances, automatic fire extinguisher systems, anywhere a safety device is called upon to operate only when a defect or malfunction occurs. The inherent defect referred to results from the mode of operation wherein the safety device, since it goes through its operational cycle only when a malfunction occurs, may rest in its deactuated, or safe, position for six months .or six years or a much longer period before it is called on to perform a safety shut-down of the controlled apparatus, and in the interim the safety device may physically deteriorate, because of rust, corrosion, accumulated dust, etc., so that after what may be years of inactivity, the safety device may be incapable of performing the safety function for which it was designed. As the design of the controlled equipment, such as oil burners, has improved over the years, the occurrence of a malfunction, such as ignition failure, is less frequent and the period of inactivity of the safety switch is prolonged thereby aggravating the difiiculty. When ignition failure, or other malfunction of the burners equipment does occur, however, the importance of a safety shut-down of the burner is not diminished by the fact that the malfunction occurs only rarely.

An object of the present invention is to provide an oil burner control circuit in which is integrated a safety switch which proceeds through its operative cycle every time the burner itself cycles, thereby avoiding the deteriorating effect of long periods of inactivity.

A further object of the present invention is to provide an oil burner control in which the safety switch, which is operated at each cycling of the burner, and the ignition timing contacts are all operated by a single warp switch assembly.

A further object is to provide an oil burner control which will recycle after the lapse of a purge time interval upon flame failure.

A further object is to provide an oil burner control utilizing a warp switch assembly which is reset at the end of each burner on-period by a resetting warp switch heater adapted to be energized only as the stack or combustion chamber temperature cools through a predetermined temperature range.

A further object is to provide an oil burner control having a simplified wiring circuit which does not require overlapping or coordinated closure of multiple combustion responsive switch contacts.

These and other objects will become apparent as the description proceeds with relation to the accompanying drawings in which:

Figure 1 is a schematic diagram of an oil burner control circuit embodying the present invention.

Figure 2 is an enlarged, fragmentary View showing details of the combustion temperature responsive switching mechanism.

Figure 3 is an enlarged, fragmentary view of the actuating portion of the combustion temperature responsive switching mechanism.

Figure 4 is a side view of the warp switch assembly.

Figure 5 is a sectional view of the apparatus of Figure 4, the section being taken generally along line VV of Figure 4.

Figure 6 is a fragmentary side view of the apparatus of Figure 4.

Figure 7 is a fragmentary view of a modified form of arrangement of the combustion responsive switching mechanism.

Figure 8 is a perspective, fragmentary view of the switch blades shown in Figure 7.

Referring initially to Figure 1, there is shown a schematic circuit diagram of an oil burner control embodying the present invention. Connected across the electrical supply lines 10 and 11 is a center-tapped transformer having a primary winding 12 and a secondary winding 13. A wire 14 connects the terminus 15 of the transformer secondary 13 with a control switch, or room thermostat 17. A Wire 18 connects the fixed contact 19 of the thermostat to one side of a relay coil 21. The other side of the relay coil is connected by means of a wire 22 to one side of a primary warp switch heater 23. The other side of the heater 23 is connected, by means of a wire 24 to one terminal of a Warp switch 26, the other terminal of the switch 26 being connected by means of a Wire 27 to the lower terminus 28 of the transformer secondary 13. Switch 29, operated to closed position upon energization of the relay coil 21, is connected to wire 22 by means of a wire 31. The other terminal of the switch 29 is connected, by means of a wire 32, to one contact 33 of a combustion responsive switch assembly 34. A contact 36, adapted to cooperate with contact 33 is connected by means of a wire 37 to an intermediate tap 38 on the transformer secondary 13. A Wire 39 connects the Wire 37 to one contact 41 of a combustion responsive switch which is operated by the same combustion responsive switch assembly 34 referred to in connection with contacts 33 and 36, as will subsequently be explained. A contact 42 adapted to cooperate with contact 41 is connected by means of a Wire 43 to one side ofaresettingwarp switchheater 44. Theother side of heater 44 is connected to one terminal of a warp switch 46 by means of wire 47. The other terminal of switch 46 is connected, by means of a wire 43, to the wire 27. Connected across the lines 10 and it is an oil burner motor of conventional type shown schematically at 49. A' burner motor switch 51, closed upon energization of relay coil 21, controls starting and stopping of the burner 49. A wire 52 connects in parallel with the burner 49 an oil burner ignition apparatus of conventional type'shown schematically A Warp switch 54 is interposed in the wire 52 and controls the energization of the ignition apparatus 53 in conjunction with the switch 51. At 56 and 57 there is shown schematic representations of bi-metal actuating elements. It will be understood the element 5'6 is warped in a left hand direction,- as viewed in Figure 1, upon energization of the resetting heater 44. Similarly, element 57 is warped in a right hand direction upon energization of primary heater 23.

As may be seen in Figures 4; 5, and 6, the primary and resetting warp switch assembly comprises an irregularly shaped mounting bracket 58 having sidewardly extending tab 59 by means of which the assembly may be mounted to a suitable mounting bracket (not shown) by any suitable means such as screw 61 (Figure 5). A stacked wiring terminal and switch blade assembly 62 is rigidly secured to the bracket 58 by means of screw 63, the switch assembly 62 being held in assembled relation by means of rivets 64. The offset portion 66 of the bracket 58 carries at its outward extremity two depending arms 67 and 68 which are notched as at 69 in Figure 4 to receive the reduced ends of a somewhat flexible blade 71. A generally L-shaped bracket 72 is held within the assembly by means of an adjusting screw 73 and a protrusion 74 in the vertical portion of the bracket 72, the front face of the protrusion 74 bearing against the blade 71 and shoulders 65 provided by notches formed in the offset portion 66 of bracket 53 which ac commodate a similarly notched portion of bracket 72. Welded, or rigidly fastened by any other suitable means, to the upper extremity of the bracket 72 is the bi-metal actuator element 56 (referred to schematically in Figure l). The resetting electrical heater 44 is mounted in a conventional manner in proximity to the element 56 so that the thermal energy generated by the heater 44 when cnergized'will warp the bi-metal 56 in a right hand direction as viewed in Figure 4. Rigidly secured to the upper extremity of the element 56 is a spacing bracket 76 which at its lower end has secured to it, by any suitable means, the bi-rnetal actuating element 57. Element 57 has secured to it an offset bracket 77 upon which is mounted the primary warp switch heater 23. The thermal energy generated by the energization of heater 23 will influence the bi-metal 57 so as to warp the upper end of I element 57 in a left hand direction, as viewed in Figure 4.

The switch assembly 62 comprises a stop member 78, an overcenter switch blade 79, carrying the movable contact of the ignition switch 54. The blade 79 is connected to an overcenter actuating blade 81 by means of an S- shaped compression member 82. It will be understood that movement of blade 81 which has the conventional central opening or slot therein permitting blade 79 to pass through it, moving member 82 through center, will serve to open and close the switch 54 with a snap action in a conventional manner. A rigid bar 33 carries the fixed contact of the switch 54. The switch assembly 62 further comprises a contact-carrying blade 84 which serves to mount the fixed contact of the switch 26. The movable contact of the switch 26 is carried by a flexible blade 86 which also carries the movable contact of the switch 46. The fixed contact of the switch 46 is carried by a bar 87.

A thrust member 55, having'reduced ends which fit thrQUgh appropriate openings in blades 84 and 79, serves to transmit movement of. blade. 79 tothe blade 84. It will be understood that blade 84 has a rightward bias (as viewed in Figure 4) which tends to open switch 26, but is held in its position of Figure 4 by the member 55. When switch blade 79 is moved through center to open switch 54, switch 26 will also open because of the inherent bias in blade 34 and because the trailing movement of blade 86 is halted by closure of switch 46. p

A link member 94 connects the upper extremity of the bi-metal element 57 with the upper extremity of the blade 2Z1 serving to transmit the motion of elements 56 and 57 to the switches 54, 26, and 46 through the blade 81 and member 55.

From the foregoing it will be apparent that upon movement of the outer extremity of element 57 to the left (as viewed in Figure 4) caused by the energization of heater 3, the switch 54 will be snapped open, switch 26 will be opened and switch 46 will be closed. Subsequentdeenergization of heater 23 and the consequent'return' of element 57 to its unheated position is not suflicient', because of the relatively wide operating differential of the overcenter mechanisrn, to move blade $1 back overcenter and switch 54 will remain open. Movement of the outer extremity of the element 56 to the right (as viewed in Figure 4) caused by energization of heater 44, will move the link 94 and consequently will eventually move blade 81 through center thereby resetting switch 54 to closed position, switch 26 to closedposition and switch 46' to open position. Again, subsequent deenergization of heater 44, and the consequent return of element 56 to its original position will, because of the relatively wide operatingdifferential of the overcenter mechanism, provide insufilcient movement for the blade 31 to move the contacts away from their reset position. If, after element 57 has opened switches 54 and 26 and closed switch 46, element 56 is not moved by means of heater 44 to reset the switch contacts, a manual means for so resetting them is provided by flexible blade 96 which is carried by switch assembly 62 and has its upper end (not shown) extending so as to be available for manual movement in a leftward direction as viewed in Figure 4. The leftward motion manually provided to blade 96 is transmitted'to the switches by means of a member 97 which has a reduced end 98 extending through an appropriate slot in the blade 96 and carries a shoulder 99 adapted to engage the blade 79 to move it through center reclosing or resetting switch 54 upon leftward movement of member 97. The end face nu of the element 97 is adapted to engage the blade 86 upon initial leftward movement of member 97, holding switch 26 and switch 46 in open position, while the blade Q6 and consequently member 97 are manually held in resetting position. This provision for holding switches 26 and 4-6 open while switch 54- is being manually reset to closed position provides a tripfree resetting function as is well known in the art.

It will be apparent that adjustment of screw 73 will vary the time required by the element 57 to open switches 54 and 26 and'close switch 46. To illustrate this adjustment, if it is assumed that screw 73'is lowered somewhat from its position of Figure 4, the bracket 72, and consequently the whole bimetal actuator assembly will be rotated slightly clockwise about the shoulders 65, the blade 71 serving to maintain bracket 72 against the lower extremity of adjusting screw '73. This change in the position of the bi-metal element assembly with relation to the switch assembly will require that the element 57 warp somewhat further to the left, as viewed in Figure 4 before switches 54 and 26 are opened.

Figures 2 and 3 disclose in detail the combustion temperature responsive switch mechanism or assembly referred to generally by reference numeral 34 in Figure I. As shown in Figure 3, the combustion switch-includes bi-metal helix 166', or similar thermal element responsive to the temperature of combustion and may extend into an area, such as the stack between the furnace andchimney, which attains a temperature which is a function of the temperature of combustion at the oil burner. One end of the element 106 is fixedly anchored to stationary element 107 and the other end is secured at 108 to an actuating shaft 109; the shaft 109 is journaled in the stationary element 1117 and rotates a collar 111 which frictionally engages a switch actuating arm 112. This frictional engagement may be obtained by utilization of a spring biased washer 113 which presses the arm 112 into engagement with the collar 111. It will be understood that since collar 111 is keyed to the shaft 1119 and since the arm 112 is loosely mounted thereon, rotation of the shaft 109 Will cause rotation of the arm 112 until movement of arm 112 is mechanically blocked, thereafter further rotation of shaft 1119 will cause slippage between the collar 111 and arm 112. This type of con nection, conventionally known as a slip friction connection, causes the movement of the arm 112 to take place in response to a change in temperature as distinguished from movement responsive to the existence of a given temperature level. The switch arm 112 is therefore rotated in one direction upon initiation of a temperature rise (clockwise as shown in Figure 1) to operate switch contact 33 into electric contact with switch contact 36, as shown in Figure 1. After contacts 33 and 36 have been closed, a continued rise in stack temperature causes the frictional connection to slip so that upon a reversal in temperature affecting the thermal element 106, the stack contacts 33 and 36 will be immediately opened.

A camming member 114 is rigidly secured to the shaft 109 and rotates with it. As may best be seen in Figure 2 member 114 has circumferentially spaced notches 116 and 117 which are adapted to accommodate indented portions of two flexible, contact-carrying blades 118 and 119 which carry at their extremities contacts 42 and 41 respectively. The base portions of blades 118 and 119 are mounted in conventional fashion in a stacked switch terminal assembly denoted generally by 121. Extending from the assembly 121, at right angles to the general direction of extension of blades 118 and 119, are member carrying contacts 36 and 33, the member 122, carrying contact 33 extends outwardly a sufiicient distance so as to be embraced by the arm 112 (Figure 3), it being understood that the switch terminal assembly 121 shown in Figure 2 is mounted beneath the member 114 of Figure 3 with member 122 co-extensive with the shaft 1139 for a portion of its length. Keeping in mind the apparatus shown in Figures 2 and 3 and referring to Figure 1, it will be apparent that, with shaft 109 in its cooled position of Figure 1, the initial rotation of shaft 1119 in response to a rise in stack temperature will immediately close the contacts 33 and 36. As the shaft 1119 rotates further in a clockwise direction (as seen in Figure 1) the member 114 will be sufficiently rotated so that notches 116 and 117 will permit contacts 41 and 42 to close. Additional clockwise rotation of shaft 109 will cause its frictional connection with arm 112 to continue slipping and will rotate notches 116 and 117 past the indentations in the blade 118 and 119 causing the contacts 41 and 42 to reopen. After the temperature of combustion has attained its steady state or running interval temperature, rotation of shaft 109 will, of course, cease and contacts 33 and 36 will be held closed and contacts 41 and 42 will be held open. At the end of an oil burner running interval, after the oil burner is shut down, the stack temperature will immediately begin to decrease and shaft 109 will be rotated counterclockwise (as viewed in Figure 1) to immediately open contacts 33 and 36. Continued decrease in the temperature to which element 106 responds will rotate element 114 in a counterclockwise direction to reclose contacts 41 and 42 for an interval which is measured by the time required for the shaft 1119 to rotate the element 114 sufiiciently for the indentations in the blades 118 and 119 to ride in and out of the notches 116 and 117 respectively. To reiterate, at the end of a burner running period, as the stack temperature begins to decrease contacts 33 and 36 and will be opened, subsequently, as the stack temperature, or the temperature brought about by combustion, decreases through an intermediate range, contacts 41 and 42 will be closed and will then be reopened as the stack temperature decreases further and the element 114 returns to its position of Figure 1. It will be noted that the indentations in member 114 are not diametrically opposite each other, but are separated by less than 180. This arrangement requires that before the contacts 4241 can be closed for the second time as the stack temperature increases, the member 114 must be rotated through 360 of rotation. In normal operation a conventional oil burner stack installation never reaches the temperature (of the order of 1250 F.) required to produce one complete revolution of member 114. Contacts 4142 are therefore closed only once as the stack. temperature increases and once as it decreases on each complete burner cycle.

At Figures 7 and 8 there is shown a modified form of the combustion responsive switch mechanism just described, parts of the modified mechanism which have counterparts in the apparatus of Figure 2 being given corresponding reference numerals but with the suflix a. As may be seen in Figure 7, the shaft 1119a carries mounted for rotation therewith a camming member 114a having a single lobe which is adapted to cooperate with the upstanding section 35 of the flexible blade which carries contact 42a. The arm 112a which has a slip friction connection with shaft 1119a is positioned so as to cooperate with the extending end 45 (Figure 8) of the blade which carries contacts 36a and 41a. In the position of Figure 7, the arm 112a has just been moved in cooling direction to open the closed-hot contacts 33a 36a and has closed contacts 41a and 42a. As the stack temperature continues to decrease, the arm 112a will contact the fixed stop 55 and the frictional connection between the arm 112a and shaft 109a will slip as the shaft 109a continues to rotate in cooling direction (counterclockwise as viewed in Figure 7).. Further rotation of shaft 10911 in cooling direction will eventually cause the lobe of member 114a to contact the section 35, further movement serving to open contacts 41a-42a. It will be apparent that at a normal oil burner shut-down, the contacts 33a-36a will immediately be opened and contacts 41a--42a will be closed and these latter contacts will remain closed until the stack temperature reaches some predetermined lowvalue, of the order of F., thereafter the contacts 41a42a will be reopened. In function the arrangement of Figure 7 differs from that of Figure 2 in that the contacts 41a-42a are closed almost immediately after the cessation of combustion, whereas in the apparatus of Figure 2 the contacts 41-42 are not closed until after the stack temperature has decreased sufficiently to rotate member 114 to align the notches 116 and 117 with the indentations in the blades 118 and 119.

Operation With the circuit components in the position shown in Figure 1, upon closure of thermostat 17 at its contact 19, indicating a call for heat, a starting circuit is completed from terminus 15 through wire 14, thermostat 17, contact 19, wire 18, relay coil 21, wire 22, primary heater 23, wire 24, switch 26, and wire 27, back to transformer terminus 28. Completion of this starting circuit energizes relay coil 21, closing switch 51 which starts the burner 49 and provides ignition for it by means of igniter 53 which is energized through the switch 54-. Energization of relay coil 21 also closes switch 29 which, however, has no immediate effect, since contacts 33 and 36, which are in series with it, are open. After combustion is established, because of the 7 increase in stack temperature, contacts 33 and 36 will be closed by the arm 112 to establish a running circuit which may be traced as follows: terminus 15, wire 14, thermostat 17, contact 19, wire18 relay coil 21, wire 22, wire 31, switch 29, wire 32, contacts 33 and 36, wire 37 back to intermediate tap 38. As the stack temperature increases further, element 114 will be rotated sufficiently to permit contacts 41 and 42 to close, however, their closure willhave no'effect on the circuit since switch 46 which is in series with them remains 1 open.

Further increase in stack temperature will cause contacts 41 and 42 to reopen as the indentations in blades li and 119 ride out of the notches 116 and 117. After a time interval from the closure of thermostat 17, which may be of the order of a minute and a half, the primary heater 23' will have caused the element 57 to warp sufliciently to open switch 54, de-energizing igniter 53, open switch 26 breaking the aforementioned starting cirwit and closing switch 46 whose closure, however, has

no effect on the circuit since contacts 41 and 42 are open. Opening switch 26 de-energizes heater 23, however, as pointed out with reference to Figure 4, though element 57 returns to its cool position, the switches 54, 26 and 46 will not be returned to their original positions because of the relatively wide operating differential of the overcenter mechanism. The burner will now operate through a normal running period which is terminated by the opening of thermostat 17, de-energizing relay 21 which opens switches 29 and 51 shutting down the burner. As soon as combustion is terminated the stack temperature begins to decrease and contacts 33 and 36 are immediately opened by the arm 112. As the stack temperature decreases further through an intermediate range of temperature, contacts 41 and 42 will be closed for an interval measured by the time requiredfor the indentations in the blades 118 and 119 to traverse the notches 116 and 117 in the element 114. This closure of contacts of 41 and 42 as the stack temperature decreases through an intermediate range, completes a resetting circuit to the resetting heater.44 which may be traced as follows: Mid-tap 38, wire 37, wire 39, contacts 41 and 42, wire 43, resetting heater 44, switch 46, wire 48 and wire 27, back to transformer terminus 28. Energization of resetting heater 44 immediately causes element 56 to warp in resetting direction to reclose ignition switch 54, reclose starting circuit switch 26, and reopen switch 46 breaking the resetting circuit. This action of element 56 returns the last mentioned switches to the standby positions of Figure l and although element 56 thereafter returns to its cooled position, as previously pointed out with reference to Figure 4, the switches 46, 26 and 54 will remain in their positions of Figure 1 because of the overcenter mechanism. Although the time interval during which the contacts 41 and 42 are closed as the stack temperature decreases is relatively short, because the resetting heater 44 is in direct contact with the bi-metal element 56 the resetting action of element 56 can be completed.

In the event of ignition failure, that is, if the burner should fail to ignite, the running circuit through contacts 33 and 36would not be established and the eventual opening of switch 26 by element 57 would break the starting circuit deenergizing relay coil 21 and shutting down the burner 49. The circuit elements would then remain in safety shutdown position, even though thermostat 17 remained closed until the switch 26, switch 54 and switch 46 were returned to their position of Figure l by manual operation of the resetting member 96 (Figure 4). burner should become extinguished during a running interval, the consequent decrease in stack temperature would almost immediately open contacts 33 and 36 breaking the running-circuit, de-energizin'g relay coil 21,

and shutting down burner- 49. As the stack tempera- In the evento'f flame failure, that is, if the t3. ture cooled through an intermediate temperature range, contacts 41 and 42 would close completing the resetting circuit and energizing heater 44 as previously described. Element 56 would thereby reset switches 54, 26 and 46 back to their positions of Figure 1. Assuming the thermostat remained closed, reclosing of switch 26 would again complete the starting circuit and the burner would proceed through its normal starting sequence. If ignition would not then occur, the circuit components would proceed to their safety shutdown or lock-out positions as previously described. It will be particularly noted that on a combustion failure, the starting circuit is not re-established through switch 26 until there has elapsed a purge interval which is composed of an increment dependent on the steady state temperature of the stack during the running interval (for example if the steady state temperature is' relatively high, a relatively longer time will elapse before the element 114 rotates counterclockwise sufiiciently to close contacts 41 and 42) and an increment which is measured by the operating time of the resettingheater and warp element 44 and 56. It should further be noted that the safety switch 26 is operated through its open and closed position with each normal operating cycle of the burner.

With the modified combustion responsive mechanism of Figure 7 utilized in the circuit of Figure 1, theaction of the control will be the same as just describedwith the exception that, on flame failure, the purge period, that is, the time elapsing between the failure of combustion and the reclosing of the starting circuit through switch 26, is made up solely by the time required for resetting heater 44 to reset'switch 26 to closed position, since the contacts Ha-42a of Figure 7 are closed immediately after cessation of combustion. The purge period, therefore, does not include an indeterminate increment which is dependent on the steady state temperature of the stack during the running interval as is the case with the mechanism of Figure 2 as previously pointed out.

The foregoing has described a preferred embodiment of the invention, modifications may occur to those skilled in the art and it is to be understood that the scope of the present invention is to be limited only by the appended claims.

I claim:

1. In a burner control system, a burner control means, a starting circuit controlling the operation of the burner control means for a starting interval and a running circuit controlling operation of the burner control means for a running interval, safety means including a switching device connected in said starting circuit movable from a first position to be latched in a second position an electrothermal operator adapted to move said switching device from said first to said second position a predetermined time after initiation of said starting interval thereby breaking said starting circuit and terminating said starting interval, combustion responsive means including a switch in said running circuit adapted to be moved in response to the establishment of combustion at the burner to complete said running circuit prior to the termination of the starting interval, and a circuit for resetting said switching device to said first position including an additional electrothermal operator .and a controlling switch operated by said combustion responsive means to complete said resetting circuit only while the temperature of said combustion responsive means decreases through a predetermined range at the end of a running interval.

2. In an oil burner control of the type having a starting and a running circuit controlling the existence of combustion at an oil burner including a switching device connected in said starting circuit adapted to be moved from a first position in which said starting circuit is completed and latched in a second position in which said starting circuit broken, a first electrothermal operator energized only when said starting circuit is completed for moving said switching device to its second position, a second electrothermal operator adapted when energized to return said switching device to its first position, and means responsive to the temperature at the burner adapted to cause energization of said second electrothermal operator only as said temperature decreases through a predetermined range after combustion has terminated, said means including a switch connected in circuit with the second electrothermal operator and'a thermally responsive operator therefor.

3. In an oil burner control of the type having a starting and a running circuit controlling the existence of combustion at an oil burner: a safety switch assembly of the type which is latched in the position to which actuated, said switch assembly having a first and second set of contacts adapted to be moved from a first position to a second position, said first set of contacts being connected in said starting circuit to complete the starting circuit in first position and to break the starting circuit in second position, a primary actuator for saidswitch assembly comprising a bimetal blade and a primary electric heater connected in said starting circuit and adapted to move said contacts from their first position to their second position, a resetting actuator for said switch assembly comprising a bimetal blade and a resetting electric heater adapted when energized to return said contacts from their second position to their first position, and a means responsive to the temperature at the burner adapted, when said second set of contacts are in their said second position, to cause energization of said resetting electrothermal operator only as said temperature decreases through a predetermined range after combustion has terminated, said means including a switch connected in circuit with the second electrothermal operator and a thermally responsive operator therefor.

4. In an oil burner control of the type having a starting and a running circuit controlling the existence of combustion at an oil burner and an ignition circuit controlling an ignition means for initiating combustion at the burner, said oil burner control including: a safety switch assembly of the type which is latched in the position to which actuated, said switch assembly having a first, second and third set of contacts adapted to be moved from a first position in which said starting circuit is completed by said first set of contacts and said ignition circuit is completed by said third set of contacts to a second position in which said starting circuit is broken by said first set of contacts and said ignition circuit is broken by said third set of contacts, a primary actuator for said switch assembly comprising a bimetal blade and a primary electric heater connected in said starting circuit and adapted to move said contacts from their first position to their second position, a resetting actuator for said switch assembly comprising a bimetal blade and a resetting electric heater adapted when energized to return said contacts from their second position to their first position, and a switch responsive to the temperature of combustion adapted to be closed within a predetermined temperature range, circuit means interconnecting said combustion responsive switch, said second set of safety switch contacts, and said resetting electric heater to cause energization of said resetting heater only as the temperature at said burner decreases through said predetermined range after combustion has been terminated.

5. In a burner control system, a starting circuit controlling the operation of a burner control relay for a starting interval and a running circuit controlling operation of the burner control rciay for a running interval, safety means including a switching device in the starting circuit movable from a first position in which said starting circuit is completed to be latched in a second position in which said starting circuit is broken and said starting interval is terminated, an electrothermal operator connected in said starting circuit for moving said switching device from said first position to said second tion a predetermined time after initiation of said starting interval, combustion responsive means including a switch in said running circuit adapted to be closed in response to the establishment of combustion at the burner to complete said running circuit prior to the termination of the starting interval, and a circuit for resetting said switching device to said first position at the end of a running interval to reinitiate said starting interval including an additional electrothermal operator and a series connected switch operated by said combustion responsive means to complete said resetting circuit only while the temperature of said combustion responsive means decreases through a predetermined intermediate range at the end of a running interval, the minimum time period between termination of a running interval and the initiation of a starting interval being thereby composed of an increment dependent on the running interval temperature of said combustion responsive means and an increment fixed by the operating time of said additional electrothermal operator.

6. In a burner control system, a starting circuit controlling the operation of a burner control relay for a starting interval and a running circuit controlling operation of the burner for a running interval, safety means including a switching device movable from a first position in which said starting circuit is completed to be latched in a second position in which said starting circuit is broken and said starting interval is terminated, an electrothermal operator connected in said starting circuit for moving said switching device from said first position to said second position a predetermined time after initiation of said starting interval, combustion responsive means including a switch in said running circuit adapted to be closed in response to the establishment of combustion at the burner to complete said running circuit prior to the termination of the starting interval, and a circuit for resetting said switching device to said first position at the end of a running interval to reinitiate said starting interval including an additional electrothermal operator and a series connected switch operated by said combustion responsive means to complete said resetting circuit only While the temperature or" said combustion responsive means decreases to a predetermined low value at the end of a running interval, the minimum time period between termination of a running interval and the initiation of a starting interval being thereby dependent solely on the operating time of said additional electrothermal operator.

References Cited in the file of this patent UNITED STATES PATENTS 1,728,314 Veitch Sept. 17, 1929 1,877,275 Cunningham Sept. 13, 1932 2,346,307 Isserstedt Apr. 11, 1944 2,385,426 Taylor et al. Sept. 25, 1945 2,567,807 Edelman Sept. 11, 1951 

